This invention relates to excavation and construction tools and is especially concerned with blocks and bits used in road maintenance construction.
Recent advances in road maintenance techniques have involved the processes of soil stabilization, asphalt reclamation, road planing and other advances that concern themselves with the conservation of materials already present in old roadbeds and the like.
Road planing, for instance, involves the mounting of bits and blocks on a power driven rotary drum. Asphalt is planed off the old road surface as the drum rotates and the bits strike or dig into the roadway. In asphalt, it is preferable to use bits that have a flat edge to shave the asphalt, rather than point-attack type bits that dig rather than scrape. This is because point-attack type bits find their greatest use in material that fractures once penetrated. Asphalt does not readily fracture once penetrated and, therefore, flat edged scraping type tools work best when road planing.
The point-attack type bits originally developed for coal mining (see U.S. Pat. No. 3,519,309) also found great use in construction type tools and other excavation type operations. One of the favorable features of the point-attack bit was the retention of the bit in its support block by a resilient split keeper ring, described more fully in U.S. Pat. No. 3,752,515.
Because the above-mentioned ring affords a very satisfactory and workable connection of the bit to the block, the use of such a ring has become almost universal in the industry. It is, therefore, desirable to retain the resilient keeper ring when designing a bit for use with road planing equipment.
Cutter bits have been designed having flat forwardly working cutting edges for road planing but retaining the cylindrical shank, clip and recess of the point-attack type tools. Rotation is resisted by tangs that entered from the bit to the block or pins may be utilized extending through the bore of the block and mating with a special flat on the shank of the bit. Some instance of rotation still occurs, probably because impacting the bit can cause it to bounce longitudinally in its holder and possibly displace any tang or other extension utilized to prevent rotation.